ABSTRACT
The use of materials as so-called smart polymers is motivated by the simple observation that biological molecules perform incredibly complex functions. While the goal of engineering polymers as effectively as nature remains somewhat in the realm of science fiction, in recent years many researchers have sought to find or design synthetic polymeric materials capable of mimicking one or another “smart” property of biopolymers. Polymer gels are promising systems for such smart functions because of their volume phase transition, predicted theoretically by Dusek and Patterson
in 1968 and experimentally demonstrated by Tanaka
in 1978. Gel collapse can be driven by any one of the four basic types of intermolecular interactions operational in water solutions and in molecular biological systems,
namely, by hydrogen
bonds and by van der Waals, hydrophobic, and Coulomb interactions between ionized (dissociated) groups. According to Flory’s theory,
the degree of swelling of a hydrogel is the result of a competition between the entropy due to polymer conformations, which causes rubber elasticity, and the energy associated with internal attractions and repulsions between the monomers in the gel and the solvent. A change in the environmental conditions, such as temperature, pH, or composition, modifies the balance between the free energy of the internal interactions and the elasticity component, inducing a volume phase transition.
